Distribution of arbuscular mycorrhizal fungi spores in soils of smallholder agroforestry and monocultural coffee systems in southwestern Ethiopia

Arbuscular mycorrhizal fungi (AMF) are associated with the root system of coffee (Coffea arabica L.) plants, but their distribution in smallholder agroforestry and monocultural coffee systems is not well known. This study investigates the spatial distribution of AMF spores in a field study in southwestern Ethiopia. Soil samples from different depths (0–50 cm) were collected under the tree canopies of Acacia abyssinica, Albizia gummifera, Ficus sur, Ficus vasta and randomly selected unshaded coffee plants at different sampling points (canopy base, radius, edge and outside canopy). Significantly higher AMF spore densities were recorded at canopy bases and at 0–30 cm soil depth. Spore populations were found to belong to five genera: Acaulospora, Entrophospora, Glomus, Gigaspora and Scutellospora, with Glomus and Acaulospora dominating. Sampling points, sites and depths, shade tree species and shade tree/coffee plant age affected AMF spore density. Agroforestry practices including the use of leguminous shade trees effectively maintained AMF numbers in soils even at depth compared with unshaded coffee plants (monocultures).     

Effect of tillage and crop on arbuscular mycorrhiza colonization of winter wheat and triticale under Mediterranean conditions

Large‐scale inoculation with arbuscular mycorrhizal fungi (AMF) is generally impractical in most regions and we have little understanding of the factors that determine inoculation success. Nevertheless, the ability to take full advantage of indigenous AMF for sustainable production needs to be developed within cropping systems. We used part of a long‐term field experiment to understand the influence of tillage and the preceding crop on AMF colonization over the growing season. Arbuscular mycorrhiza colonization rate was more affected by treatment (tillage or the combination of crop and preceding crop) than by the total number of AMF spores in the soil. Conventional tillage (CT) had a statistically significant negative effect (P ≤ 0.05) on spore numbers isolated from the soil, but only in the first year of study. However, the AMF colonization rate was significantly reduced by CT, and the roots of wheat, Triticum aestivum, L, cv. Coa after sunflower, Helianthus annuus L., were less well colonized than were those of triticale, X Triticosecale Wittmack, cv. Alter after wheat, but the affect of tillage was more pronounced than was the effect of crop combination. Under no‐till there was a significant increase in AMF colonization rate throughout the sampling period in both wheat and triticale, indicating that the extraradical mycelium previously produced acted as a source of inoculum. In general, triticale showed greater AMF colonization than wheat, despite the preceding crop being less mycotrophic. Under these experimental conditions, typical of Mediterranean agricultural systems, AMF colonization responded more strongly to tillage practices than to the combination of crop and preceding crop.     

长期保护性耕作对丛枝菌根真菌多样性的影响

为了明确我国北方干旱地区长期保护性耕作以及深松对丛枝菌根真菌(AMF)多样性的影响,笔者于2014年在山西省临汾市连续22年实施保护性耕作的长期定位试验基地,针对免耕覆盖(NTS)、深松免耕覆盖(SNTS)及传统耕作(TT)3种处理方式,进行了不同耕作条件下土壤AMF物种丰度、孢子密度、Shannon多样性指数以及AMF侵染率等因素的比较研究。结果显示,长期保护性耕作(NTS和SNTS)共分离鉴定出AMF 7属9种,其中根孢囊霉属(Rhizophagus)和斗管囊霉属(Funneliformis)各2种,球囊霉属(Glomus)、近明球囊霉属(Claroideoglomus)、无梗囊霉属(Acaulospora)、硬囊霉属(Sclerocystis)和隔球囊霉属(Septoglomus)各1种;而传统耕作(TT)共分离鉴定出AMF 6属8种,没有检测到无梗囊霉属。NTS、SNTS和TT处理在不同土层的AMF优势种基本一致,0~40 cm土层为摩西斗管囊霉(Fu.mosseae)和变形球囊霉(G.versiforme),40~80 cm土层为摩西斗管囊霉、变形球囊霉和聚丛根孢囊霉(Rh.aggregatum),80~120 cm土层为聚丛根孢囊霉,120 cm土层以下只有NTS和SNTS处理中存在聚丛根孢囊霉,说明保护性耕作措施促进了AMF向土壤深层发展。NTS和SNTS处理在同一土层的AMF物种丰度、孢子密度和Shannon多样性指数均高于TT处理,SNTS处理高于NTS处理。同一耕作措施不同土层的AMF物种丰度、孢子密度和Shannon多样性指数均随土层加深而逐渐降低;NTS和SNTS处理在小麦各生育期的丛枝侵染率和孢子密度均高于TT处理;各处理在小麦拔节期的AMF侵染率最高,分别为14.9%、16.1%和10.6%,而在收获期的土壤孢子密度最高,分别为111.7个·(100g)~(-1)、125.0个·(100g)~(-1)和90.3个·(100g)~(-1)。研究认为,长期免耕覆盖、尤其深松免耕覆盖,提高了AMF多样性。该研究结果可为中国北方旱作农田生态系统中AMF自然潜力的充分发挥,以及保护性耕作技术的合理应用提供科学依据。     

Vesicular-arbuscular mycorrhizae in tropical sedges of southern India

Twenty-four species of sedges (representing six genera) from different vegetation types in Western Ghats, South India, were examined for vesicular-arbuscular mycorrhizal (VAM) associations. All the sedges had VAM fungal infections with hyphae and vesicles, but arbuscules were observed only in 42% of the total species. The VAM fungal colonization varied considerably between species, ranging from 9 to 62%. Root colonization was positively and negatively correlated with root diameter and root hair length, respectively. The number of VAM fungal spores in the rhizosphere varied from 5 to 86 g^-1 soil. No significant relationship was found between spore numbers or root colonization and either soil pH or moisture. Four Glomus spp., one Acaulospora sp., one Sclerocystis spp., and one Gigaspora sp. were identified among the VAM fungal spores. The results reflect a high incidence of VAM in sedges occurring in Western Ghats and emphasize the need to assess the VAM status of plant species from different ecosystems to understand their mycorrhizal status.     

Arbuscular mycorrhizal fungal community structure and diversity in response to 3-year conservation tillage management in a sandy loam soil in North China

Purpose

Modern agricultural science has greatly reduced the use of tillage. Monitoring conservation versus conventional tillage effects on soil microbes could improve our understanding of soil biochemical processes and thus help us to develop sound management strategies. The objective of this study was to investigate the effects of conservation tillage on the spore community structure and the diversity of soil arbuscular mycorrhizal (AM) fungi and to find out the main factors that influence these parameters.

Materials and methods

A long-term field experiment established in a sandy loam soil in Northern China has received continuous tillage management treatments for 3?years, including conventional tillage (CT), no tillage (NT), and alternating tillage (AT). Topsoil samples (0?C15?cm) from four individual plots per treatment were collected for the analysis of chemical properties and fungal parameters. AM fungal spores were isolated using the wet-sieving method and identified to species level based on morphology by light microscopy. The community structure and the diversity of AM fungi were evaluated using the following parameters: spore density, relative abundance, species richness, Shannon?CWiener index (H??), evenness (E), and Simpson's index (D). Jaccard index (J) of similarity was calculated to compare AM fungal species composition under different treatments.

Results and discussion

Twenty-eight species of AM fungi within four genera, Glomus, Acaulospora, Scutellospora, and Entrophospora, were recovered from the 12 plots within the three tillage management treatments. Higher spore density, species richness, and species diversity (H??, E, and D) of AM fungi were observed in the two conservation tillage treatments, and the redundancy analysis showed that the species richness significantly correlated to soil organic carbon content (P?<?0.05). The positive effects of NT and AT on the species richness were very close, while the AT had relatively greater beneficial impacts on the spore density and the evenness of AM fungi compared to the NT. The lowest Jaccard index (J) of similarity in species composition was also observed between the AT and CT treatments.

Conclusions

Soil organic carbon, the spore density, and species richness and diversity of AM fungi increased in the two conservation tillage treatments. The species richness of AM fungi significantly correlated to soil organic carbon content (P?<?0.05). Compared with the CT treatment, the AT rather than the NT significantly increased the spore density and the evenness of AM fungi (P?<?0.05). Thus, alternating tillage practice may be more beneficial to agroecosystem in this region.     

Arbuscular mycorrhizal associations in sesame under low-input cropping systems

The abundance and composition of arbuscular mycorrhizal fungi (AMF) are generally low under managed agroecosystems in comparison to natural ecosystems. The objective of the study was to determine the composition and species richness of AMF associated with sesame under traditional low-input cropping system in Kerala, India. Wide variability in root colonization by AMF as well as spore density in the rhizosphere existed in sesame. Correlation between frequency of colonization (F%) and spore density as well as between these variables and soil characteristics showed a negative relationship. The fungal variables were influenced by soil factors such as pH, soil organic carbon (OC) and available nutrients. Frequency of colonization was positively correlated (P < 0.01) with soil pH and potassium (K) and negatively correlated with OC, nitrogen (N) and phosphorus (P). AM spore density was positively correlated with OC, N and P and negatively correlated with pH and K. Ten taxa of AMF belonging to the genera Acaulospora, Diversispora, Funneliformis, Gigaspora, Glomus and Scutellospora were associated with sesame, with the predominance of Funneliformis and Acaulospora in both frequency and relative abundance over a wider soil nutrient range. Soil characteristics appear to have a profound influence on the composition and species richness of AMF under traditional low-input cropping systems.     

巴西大西洋森林中巴西松地面根部显示丛枝菌根真菌高定殖率和多样性

Almost 30 different arbuscularmycorrhizal fungi (AMF)species, distributed in different genera such as Glomus, Acaulospora,Scutellospora,Entrophospora,Ambispora,Kuklospora,Gigaspora,and Archeospora, have been identified in the root zone of Araucaria angustifolia, known as Brazil Pine. During our AMF survey in this ecosystem, our attention was called to the presence of many superficially growing Araucaria roots. Our hypothesis was that these roots were colonized with AMF because of the presence of AMF spores in organic material aboveground. Samples of these superficial roots and the organic substrate they were growing on were evaluated for their mycorrhizal status. DNA was extracted from the AMF colonized superficial roots and submitted to polymerase chain reaction (PCR) amplification using the NS31-AM1 primer pair, followed by cloning and sequencing. We found that the root colonization percentages were between 31% and 52%, and the number of AMF spores in the substrate ranged from 27 to 164 spores per 50 g dry substrate.The phylogenetic analyses and tree construction using maximum parsimony (MP) and neighbor-joining (NJ) methods identified 13 different species of the phylum Glomeromycota belonging to the genera Glomus, Funneliformis, Rhizophagus, Gigaspora, Acaulospora,and Archaeospora, and five isolates were identified only at the genus level. To our knowledge, this is the first report on Araucaria angustifolia with roots growing aboveground, producing runner roots that develop on dead tree trunks and organic material. The higher colonization of the aboveground roots than those commonly found in belowground Araucaria roots suggests that they may present active metabolic uptakeof nutrients.     

Species composition of arbuscular mycorrhizal fungi in two mountain meadows with differing management types and levels of plant biodiversity

Species composition of arbuscular mycorrhizal fungi (AMF) was analysed in two differently managed mountain grasslands in Thuringia (Germany). Arbuscular mycorrhizal fungi were studied in the roots of 18 dominant plant species from a total of 56 (32%). Additionally, spores of AMF were isolated from soil samples. Arbuscular mycorrhizal fungi species composition was analysed based on 96 sequences of the internal transcribed spacer of the nuclear ribosomal DNA, 72 originated from mycorrhizal roots, and 24 originated from AMF spores. Phylogenetic analyses revealed a total of 19 AMF species representing all genera of the Glomeromycota except Scutellospora and Pacispora. Despite a different farming intensity, resulting in remarkable differences concerning their plant species diversity (27 against 43 plant species), the diversity of AMF was found to be similar with 11 species on the intensively farmed meadow and ten species on the extensively farmed one. Nevertheless, species composition between both sites was clearly different. It thus seems likely that the AMF species composition, but not necessarily the species number, is related to above ground plant biodiversity in the system under study.     

Arbuscular mycorrhizal fungal communities associated with some pioneer plants in the lahar area of Mt. Pinatubo,Philippines

An extensive area has been buried due to the repeated occurrence of mud flows (lahars) derived from volcanic deposits during the eruption of Mt. Pinatubo in the Philippines. Most of the area was covered with sparse vegetation consisting of only a few gramineous pioneer plants such as Saccharum spontaneum (site SV). However dense vegetation consisting of wild leguminous plants such as Calpogonium mucunoides showed a patch distribution (site DV). In 1999, we investigated the community composition of AMF at these two sites. S. spontaneum at both sites was slightly colonized with AMF while the leguminous plants were highly colonized. Spores of AMF were collected from the rhizosphere of these plants. Eight spore morphotypes were identified; one each for Acaulospora and Entrophospora colombiana, two for Glomus, one for Paraglomus, and three for Scutellospora. Part of the 18S rRNA gene of AMF colonizing the plant roots was amplified with AMF-specific primers, NS31 and AM1, cloned and sequenced. Fifty-three AMF clones were phylogenetically classified into 8 phylotypes as follows: one each for Acaulospora and E. colombiana, five for Glomus, and one for Scutellospora. Both molecular and morphological examinations showed that the diversity of AMF was comparable to that in other temperate ecosystems with abundant vegetation and did not differ significantly between sites SV and DV, regardless of the vegetation cover. Furthermore, S. spontaneum supported diverse AMF species in spite of its scant growth at site SV. E. colombiana was mostly associated with C. mucunoides. Significance of AMF for the primary plant succession in the lahar area was analyzed.     

Association between Burkholderia species and arbuscular mycorrhizal fungus spores in soil

Burkholderia pseudomallei, the bacterial cause of the potentially fatal infection known as melioidosis, has a facultative intracellular lifestyle. The intracellular presence of B. pseudomallei in various eukaryotes including arbuscular mycorrhizal fungus (AMF) spores can be demonstrated in vitro. AMF spores were isolated from soils in a melioidosis-endemic area. B. pseudomallei and other Burkholderia spp. DNA was detected in these AMF spore samples, confirming an AMF spore-Burkholderia spp. association in soils which did not yield Burkholderia spp. by culture. This association may explain the environmental persistence, difficulty of recovery and dispersal of Burkholderia spp. in specific environments.     

Bacteria associated with Glomus clarum spores influence mycorrhizal activity

The effects of bacteria associated with arbuscular mycorrhizal fungal (AMF) spores on spore germination, growth in vitro and on the pea-AMF symbiosis were evaluated. Bacterial colonies were recovered from untreated Glomus clarum NT4 spores and NT4 spores decontaminated with 5% chloramine-T for 30, 45 and 60 min on five different media. Both G+ and G− bacteria were recovered from untreated NT4 spores, whereas only G+ bacteria were isolated from decontaminated spores. An in vitro assessment of the effect of spore-associated bacteria on clean, decontaminated NT4 spores revealed that (i) most of the bacteria isolated from untreated spores generally did not significantly alter spore function, (ii) some bacteria isolated from clean, decontaminated spores inhibited or stimulated NT4 spore germination, (iii) stimulation of spore germination occurred only when bacteria were in contact with spores, and (iv) inhibition of spore germination was the result of volatile bacterial metabolites. A stimulatory bacterial isolate, Bacillus pabuli LA3, significantly (P<0.05) enhanced the shoot growth, AMF-colonization, shoot N content and P use efficiency of NT4-inoculated 6 week-old pea plants over that of plants co-inoculated with an inhibitory bacterial isolate, Bacillus chitinosporus LA6a and NT4.     

Differential growth response of Curculigo orchioides to native arbuscular mycorrhizal fungal (AMF) communities varying in number and fungal components

The study reports diversity of arbuscular mycorrhizal fungal (AMF) species in the rhizosphere of an endangered anticancerous herb – Curculigo orchioides Gaertn. in its natural habitat. A total of 18 species of AMF, belonging to three genera (Acaulospora, Glomus and Gigaspora) were recorded, with Glomus microcarpum being the most abundant species type. The AMF species composition across the study sites appeared to be influenced by soil pH rather than soil P and vegetation. Acaulospora laevis spores were restricted to sites where the soil pH was acidic. The effectiveness of these native AMF species on growth performance of C. orchioides plants was compared under experimental conditions. In general, the mycorrhizal plants were superior in most of the evaluated parameters, but the extent to which the growth of mycorrhizal plants was influenced varied with the inocula used. The plants inoculated with mixed consortia containing maximum AMF species richness exhibited improved growth in comparison to consortia containing lower AMF diversity and monospecies cultures. The variable plant responses observed with any two consortia having same species richness in the present study could be due to variable component AMF species and their relative abundance. These results emphasize the need to protect the below-ground diversity of AMF and recommend their usage for restoration practices.     

不同轮耕方式对渭北旱塬麦玉轮作田土壤物理性状与产量的影响

为研究不同轮作模式对渭北旱作冬小麦?春玉米一年1熟轮作田土壤物理性状和产量的影响,于2007—2014年在陕西省合阳县冬小麦?春玉米轮作田连续7年实施了保护性耕作定位试验,测定和分析了免耕/深松、深松/翻耕、翻耕/免耕、连续免耕、连续深松和连续翻耕6种轮耕模式下麦田0~60 cm土层物理性状、0~200 cm土层土壤湿度和小麦产量的变化。结果表明:1)不同轮耕模式0~40 cm土层土壤容重、孔隙度和田间持水量差异显著,其中以免耕/深松效果最显著;0~60 cm土层免耕/深松轮耕处理平均田间持水量较连续翻耕处理提高12.9%;2)轮耕对土壤团聚体特性影响明显,免耕/深松0.25 mm水稳性团聚体含量(R0.25)最高,结构体破碎率和不稳定团粒指数(ELT)最低,水稳性均重直径(WMWD)最高,水稳性和力稳性团聚体分形维数(D)均最低;3)小麦生育期间免耕/深松处理0~200 cm土层土壤蓄水量和小麦产量较连续翻耕分别增加17.7 mm和9.5%。综合可知,轮耕有利于耕层土壤物理结构改善,免耕/深松更有利于耕层土壤大团聚体形成和土壤结构稳定,利于土壤蓄水保墒和作物增产,为渭北旱塬区麦玉轮作田较适宜的轮耕模式。     

Molecular identification of arbuscular mycorrhizal fungal spores associated to the rhizosphere of Retama raetam in Tunisia

ABSTRACT

Arbuscular mycorrhizal fungi (AMF) are found in the soil of most ecosystems where they form mutualistic associations that affect plants growth. We have investigated the community structure of AMF associated to Retama raetam growing in five regions of Tunisia. The total number of spores was significantly different across sites, ranging from 633 to 1062 spores per 100 g dry soil. A dominance of small spores was revealed. The large subunit region of the rDNA of AMF spores associated to the rhizosphere of R. raetam was sequenced. Sequences clustered into 13 operational taxonomic units. Phylogenetic analysis revealed that the majority of sequences were grouped within Glomeraceae and Claroideoglomeraceae families. Only two sequences were affiliated to the Scutellospora genus. These results suggest the dominance of the genus Glomus in the soil rhizosphere of R. raetam. A correlation between phylogenetic analysis, soil chemicals properties, and AMF community richness was also detected.     

Arbuscular mycorrhizal fungi in the Brazilian Atlantic forest: A gradient of environmental restoration

Arbuscular mycorrhizal fungi (AMF) are of great importance for the successful regeneration of degraded natural areas. The objective of this study was to examine how the time of environmental recuperation is affecting the occurrence and diversity of AMF species in riparian areas belonging to the Atlantic Forest biome in the State of São Paulo, Brazil. The study involved a native forest area (NT) and a gradient of environmental restoration: five (R05), ten (R10), and twenty (R20) years after reforestation. Soil samples were collected in the rainy (January) and dry season (June). Chemical, physical and microbiological analyses were performed including the amount of glomalin and quantification of AMF spores. The frequency of occurrence of genera and ecological indices, as richness (R), Shannon's diversity (H) and Simpson's dominance index (Is) were calculated. The largest spore number was found in R05 and the highest richness and diversity indices of AMF species in NT. Considering the two sampling periods and the four areas studied, we found 22 AMF species, and the genera Glomus and Acaulospora were the most frequent. A Canonical Discriminant Analysis showed that Glomus viscosum, Acaulospora scrobiculata, Acaulospora mellea and Scutellospora heterogama were the species that contributed the most to distinguishing the areas. Moisture, density and glomalin were positively correlated with the number of spores, however, soil nitrate showed a negative correlation. This work gives a better understanding of the interactions between AMF and forest soils and allows to know the distribution of AMF species according to environmental recovery time.     

Soil sustainability indicators following conservation tillage practices under subtropical maize and bean crops

Conservation management systems such as no tillage may enhance sequestration of soil C. The soil properties that contribute to soil C storage under such systems are still largely unknown, especially in subtropical agroecosystems. We investigated the influence of tillage [mouldboard plough (MP) and no tillage (NT)] on soil organic C, microbial biomass and activity, structural stability and mycorrhizal status of a field cultivated with maize (Zea mays L.) or bean (Phaseolus vulgaris L.) on a Vertisol in Northern Tamaulipas, Mexico. Crop type, tillage system and soil depth had a significant effect on soil organic C, aggregate stability and bulk density. Soil organic C, microbial biomass C and N and dehydrogenase and phosphatase activities were greater with NT than with MP, particularly under bean cultivation. In the 0–5 cm layer, microbial biomass C and N were, on average, about 87 and 51% greater in the soils cultivated with bean and maize, respectively, under NT than under MP. Higher levels of mycorrhizal propagules, glomalin related soil protein (GRSP) and stable aggregates were produced under NT than under MP in both crops. The no-tillage system can be considered an effective management practice for carrying out sustainable agriculture under subtropical conditions, due to its improvement of soil physical and biochemical quality and soil C sequestration.     

Impact of a 5-year winter cover crop rotational system on the molecular diversity of arbuscular mycorrhizal fungi colonizing roots of subsequent soybean

The impact of winter cover crops, specifically wheat (Triticum aestivum L.), red clover (Trifolium pratense L.), and rapeseed (Brassica napus L.) or winter fallow, on community composition of arbuscular mycorrhizal fungi (AMF) in subsequent soybean roots was investigated in a 5-year field trial on andosolic soils in Japan. Soybean roots were sampled at full-flowering and analyzed for AMF communities using a partial LSU rDNA region. Phylogenetic analysis detected 22 AMF phylotypes, including eight Glomus, three Gigaspora, two Scutellospora, three Acaulospora, two Rhizophagus, and one of Funneliformis, Diversispora, Paraglomus, and an unknown glomeromycete in the roots. The 5-year rotation of different winter cover crops or winter fallow did not impact the molecular diversity of AMF communities colonizing the roots of subsequent soybean. In all of the rotations, Glomus and Gigaspora phylotypes were common to soybean roots over the 5-year period. Redundancy analysis (RDA) demonstrated that AMF communities in the roots of subsequent soybean were not significantly different among winter cover crop rotations or fallow. However, AMF communities in soybean roots were clearly influenced by rotation year suggesting that climate or other environmental factors were more important than winter cover cropping system management.     

Screening of Arbuscular Mycorrhizal Fungi for Symbiotic Efficiency with Sweet Potato

A greenhouse study was conducted to study the efficiency of 14 isolates of arbuscular mycorrhizal (AM) fungi isolated from a local agricultural soil on the productivity of sweet potato (Ipomoea batatas). The different AM fungi enhanced the biomass and nutritional status of sweet potato seedlings to different extents. The genus Glomus was more effective than Acaulospora or Scutellospora. Efficiency also varied among isolates of Glomus irrespective of individual host plant or location of origin. Intraspecific differences were sometimes greater than interspecific differences. Benefits deriving from fungal isolates were positively correlated with the root-colonization rate and the abundance of extraradical propagules of the AM fungi. Taking plant yield parameters, nutritional status of the plants, and fungal attributes into consideration, GEGM (Glomus etunicatum together with Glomus mosseae) and GE6 (Glomus etunicatum) were the most effective AM symbionts for sweet potato under the experimental conditions.     

Soil tillage and herbicide applications in pea: arbuscular mycorrhizal fungi,plant growth and nutrient concentration respond differently

ABSTRACT

We conducted a field- and pot experiment with peas to investigate the impact of soil tillage and herbicide applications on arbuscular mycorrhizal fungi (AMF), plant growth, phosphorus concentrations, C:N ratio in plants and yield. The field study was carried out in a long-term soil tillage experiment where four tillage treatments have been compared. Field soil from the experimental plots were used for the pot experiment. AMF were not affected by herbicide (MCPB) application, neither in the field nor in the pot experiments. However, AMF root colonization was enhanced by reduced tillage, minimum tillage and no-tillage practices, compared to conventional tillage. In the pot experiment, plant growth and nodulation of pea roots was negatively affected by the high herbicide dosage. In the field experiment neither tillage nor herbicide treatment exert specific effects on root growth parameters, phosphorus concentrations, C:N ratio and plant dry matter. This work demonstrates that an appropriate herbicide usage coupled with conservation soil tillage techniques can favour AMF root colonization and benefit plant growth.

Abbreviations: AMF: arbuscular mycorrhizal fungi; CT: conventional tillage; RT: reduced tillage; MT: minimum tillage; NT: no tillage; P: Phosphorus; C:N ratio: carbon:nitrogen ratio     

长期定位施肥对丛枝菌根真菌多样性的影响

Diversity of arbuscular mycorrhizal fungi (AMF) was investigated in a field that had received long-term fixed ferti-lization (LFF) for 26 years.There were a total of 12 treatments in triplicates with different amounts of manure,urea,calcium phosphate,and potassium chloride.Rhizosphere soil samples of maize and wheat grown in the experimental field in Shandong Province,China,were collected in September 2003 and May 2004,respectively.Arbuscular mycorrhizal fungal spores were isolated and identified using morphological characters.Mycorrhizal colonization percentage,spore density (SD),species richness (SR),relative abundance (RA),and Shannon-Weiner index (SWI) were determined.Nineteen recognized species of AMF belonging to 5 genera were identified.Long-term fixed fertilization significantly influenced colonization percentage,SR,SD,and species diversity of AMF.The adaptability of AMF to soil fertility was different among species.Species richness and SD of AMF in maize and wheat rhizosphere soils were the highest in the nonferti-lization treatment (control) and lowest in the high manure + high nitrogen treatment (M₂N₂).The SWI decreased as the fertilization level increased except in the low manure treatment (M₁) on maize.Compared with the other treatments,Treatment M₂N₂ significantly reduced SD of Glomus,and the high manure + low nitrogen treatment (M₂N₁) significantly retarded sporulation of Scutellospora.Manure treatments stimulated sporulation of Glomus mosseae.Spore density of G.mosseae was higher in the high nitrogen + phosphorus + potassium treatment (N₂PK) than in the high nitrogen + phosphorus treatment (N₂P) and the high nitrogen + potassium treatment (N₂K).The SD of S.pellucida was higher in Treatment N₂K than Treatments N₂PK and N₂P.In conclusion,long-term fixed fertilization,especially with high levels of manure and N,decreased SR,SD,and colonization and changed the species composition of AMF.